コリオリ力

The Coriolis force is a fictitious force that acts on objects moving within a rotating reference frame. It arises because the equation of motion in a non-inertial rotating frame differs from that in an inertial frame. The Coriolis force is proportional to the cross-product of the rotating frame's angular velocity vector and the object's velocity vector, and it modifies Newton's Second Law in rotating systems.

To find the Coriolis force direction, use the right-hand rule for cross-products. Point your index finger toward the object's velocity and your thumb toward the rotating frame's angular velocity. Your middle finger then points opposite to the Coriolis force, as indicated by the negative sign in the force expression. This method applies regardless of rotation direction.

In the rotating reference frame, fictitious forces including the Coriolis force act on the ball, modifying its trajectory. A ball sliding on a counterclockwise rotating turntable curves toward the right due to the Coriolis force deflection. If the table rotates clockwise, the ball deflects toward the left, demonstrating how the Coriolis force depends on the rotation direction.

Due to Earth's rotation, the Coriolis force deflects moving bodies rightward in the northern hemisphere and leftward in the southern hemisphere. This deflection affects long-range projectiles and contributes to cyclone formation, where air swirls clockwise around high-pressure systems and counterclockwise around low-pressure regions in the northern hemisphere. At the equator, the Coriolis force is zero, preventing cyclone formation.

No, the Coriolis force does zero work on a moving object because it always acts perpendicular to the object's motion. Since work equals force dot displacement, and perpendicular vectors have zero dot product, the Coriolis force cannot change an object's kinetic energy, only its direction of motion.

Both Coriolis and centrifugal forces are fictitious forces acting in non-inertial rotating reference frames. The centrifugal force depends only on the object's position and the frame's angular velocity, while the Coriolis force depends on the object's velocity relative to the rotating frame. Together, they modify the equation of motion in rotating systems.

Italian military officers in 1651 observed that cannon balls consistently landed to the right of predicted positions during artillery practice. This phenomenon was later explained by French mathematician Gaspard Gustave Coriolis (1792–1843), whose work on rotating reference frames led to naming the force after him. The deflection demonstrated the Coriolis force's significant effect on projectile motion.